Lubricant compositions

ABSTRACT

LUBRICANT ARE STABILIZED AGAINST OXIDATION BY ADDING AN ANTIOXIDANT AMOUNT OF A COPOLYMER OF A DIALKYL HYDROCARBYLPHOSPHONATE AND AN LARYLIMINO DIALKANOL.

United States Patent O 3,654,157 LUBRICANT COMPOSITIONS Gerassimos Frangatos, Westmont, N.l., assignor to Mobil Oil Corporation No Drawing. Filed July 15, 1970, Ser. No. 55,261 Int. Cl. Cm N46 US. Cl. 252-493 9 Claims ABSTRACT OF THE DISCLOSURE Lubricants are stabilized against oxidation by adding an antioxidant amount of a copolymer of a dialkyl hydrocarbylphosphonate and an arylimino dial-kanol.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to lubricating oils having desirable oxidative properties. The invention relates more particularly to the improvement of such lubricating oils by incorporating therein additives which are eifective in improving the oxidative stability properties of such oils.

Description of prior art Lubricating oils are subject to oxidative deterioration at elevated temperatures or upon prolonged exposure to the elements. These lubricants, including mineral oils and synthetic oils, undergo oxidative deterioration in service, especially at high temperatures. This deterioration produces sludges and gums, causes metal parts to corrode and produces loss of lubricating properties of the oil. Many additives of the prior art are only marginally effective except at high concentrations, especially when the oils are subjected to drastic oxidizing conditions.

SUMMARY OF THE INVENTION In accordance with this invention, there is provided a lubricating oil composition comprising a major amount of oil and an amount sufficient to impart oxidative stability thereto of a copolymer of a dialkyl hydrocarbylphosphonate and an arylimino dialkanol.

DESCRIPTION OF SPECIFIC EMBODIMENTS The aforementioned copolymer is produced by a condensation reaction, so it is important that a 1:1 molar ratio of phosphonate to dialkanol be maintained. The reaction produces a copolymer believed to be made up of the following unit recurring along the polymer chain:

wherein n is a from 2 to about 200 and R, R and Ar are as hereinafter defined in connection with the starting materials.

In general, the invention contemplates the use of from about 0.005 to about of the additive in the composition. Preferably, the concentration of additive in such oil will be from about 0.01 to about 10% by weight thereof, and more preferably from about 1.0% to about 5.0%.

The lubricants which may be improved by the addition thereto of the above-mentioned copolymer are mineral oils, both paraffinic and naphthenic, and synthetic oils. The synthetic oils include polyolefin fluids, polyglycols, polyacetals, the siloxanes and the like. Especially useful are those synthetic esters which are becoming more and more popular, particularly in aviation. These include esters made from polycarboxylic acids and monohydric alcohols, such as those obtained by reacting methanol, ethanol, propanol, butanol, neopentyl alcohol and the like with pimelic acid, azelaic acid, adipic acid and the like, or from polyhydric alcohols and monocarboxylic acids. Of these preferred members are those made from trimethylol alkanes, where alkane includes ethane, propane and butane, pentaerythritol, diand tripentaerythritol, or mixtures thereof and an aliphatic monocarboxylic acid containing from 1 to about 20 carbon atoms or a mixture of such acids. The most preferred are esters from the pentaerythritols and monocarboxylic acids having from 5 to 9 carbon atoms, or mixtures of these acids.

Broadly speaking, the copolymers contemplated herein may be prepared by blending phosphonate and dialkanol, or by blending these with a small quantity of an alkali metal, in an inert organic solvent, and heating to effect reaction. The time of reaction will range from about 1 hour to about 20 hours, and during this time the reaction may be effectively carried out at temperatures between about 50 C. and 225 C., preferably from about C. to about C.

Any of the well-known solvents may be used in preparing the copolymer. One example of a useful solvent is xylene. Others include chlorobenzene, benzene, toluene, mesitylene, dioxane and carbon disulfide.

The dialkyl hydrooarbylphosphonates contemplated are those having the formula wherein R may be alkyl, aryl, aralkyl and cycloalkyl and may contain from 1 to about 200 carbon atoms, preferably from 1 to about 50 carbon atoms and R may be individually selected from alkyl groups having from 1 to about 10 carbon atoms. Since the reaction involves transesteriification with consequent removal of an alkanol, it is referred that R be kept from 1 to about 6 carbon atoms, and more preferably from 1 to about 3 carbon atoms. Included among the phosphonates which may be used as one of the reactants are dimethyl methylphosphonate, dimethyl ethylphosphonate, dimethyl decylphosphonate, dimethyltetradecylphosphonate, diethyl octadecylphosphonate, diethyl triacontylphosphonate and dipropyl pentacontylphosphonate. Included also are phosphonates in which the (R, groups are different. As examples there may be mentioned methyl ethyl octylphosphonate, ethyl propyl triacontylphosphonate and the like. Furthermore, phosphonates exemplified by dimethyl phenylphosphonate, diethyl cyclohexylphosphonate, dipropyl benzylphosphonate and the like are contemplated.

The arylimino dialkanols contemplated in this invention are those having the formula ArN R"OH) 2 wherein Ar is an aryl group having from 6 to 30 carbon atoms in the ring or condensed ring portion thereof and which may have substituted thereon an alkyl group of from 1 to about 50 carbon atoms, a nitro, halo (preferably chloro, iodo or fluoro) or cyano group, and R" is an alkylene having from 1 to about 50 carbon atoms.

Among those arylimino dialkanols which can be used in practicing this invention are: phenylimino diethanol, dipropanol, dibutanol, didecanol, and the like; naphthylimino diethanol, dipropanol, dibutanol, and the like; chlorophenylimino dimethanol, diethanol, dipropanol, dipentanol and the like; and nitrophenylimino dimethanol, diethanol, dipropanol and the like.

The following examples will serve to specifically illustrate the practice of the invention. It will be understood that they are illustrative only, and are not intended to limit the scope of the invention to a narrower range than described hereinabove.

EXAMPLE 1 Xylene (250 ml.) was charged to a reaction flask. To this were added 1.1 g. of metallic sodium, 36.1 g. (0.1 mole) of dimethyl octadecylphosphonate and 18.1 g. (0.1 mole) of 2,2-phenylimino diethanol while maintaining an atmosphere of nitrogen over the reaction medium. Thereafter, the reaction mixture was heated to 140 C. and maintained at this temperature for 6 hours. The solvent was slowly distilled under atmospheric pressure. It contained the theoretical amount of methanol (6.4 g., 0.2 mole) determined by Gas Liquid Chromatography (GLC). The remaining traces of solvent were removed in vacuo at 200 C. and 0.65 mm. of Hg. 45.3 g. of prod uct was obtained. The stoichiometry of the reaction, the quantity of the methanol recovered and the yield of final product indicated that a condensation copolymer was obtained.

The dimethyl octadecylphosphonate used in this example was prepared by reacting l-octadecene and dimethyl phosphonate at a 1:3 molar ratio in the presence of ditertiary butyl peroxide. Specifically the phosphonate and l-octadecene were mixed, heated to 150 C. and the peroxide was added dropwise over a period of 30 minutes. Following addition of the peroxide, the reaction was completed by heating the reaction mixture for 60 minutes at 150 C.

EVALUATION OF PRODUCTS Oxidation test The compounds produced in accordance with this in vention were blended into a synthetic ester oil lubricant (made by reacting pentaerythritol with an equimolar mixture of C and C monocarboxylic acids) and tested in an oxidation test in accordance with the following procedure.

A sample of the test composition is heated and air at the rate of about 5 liters per hour is passed through for a period of about 24 hours. Present in the test sample are specimens of iron, copper, aluminum, and lead. The kinematic viscosity is measured at 100 F. (percent KV change) and the change in the neutralization number (NN change). It should be noted that the metals are typical metals of engine or machine construction, and they also provide some catalysis for the oxidation of organic materials. The results, tabulated in the following table, concern the product of Example 1.

Percent Temp., Initial Final A Initial Final AKV, ditive F. NN NN NN KV KV percent I claim:

1. A lubricating oil composition comprising a major amount of a lubricating oil and an amount sufficient to impart antioxidant properties thereto of a copolymer produced by reacting, in a 1 to 1 molar ratio, (1) an arylimino dialkanol of the formula wherein Ar is an aryl group having from 6 to about 30 carbon atoms or a substituted aryl group, where the substituent is selected from the group consisting of alkyl having from 1 to about carbon atoms, nitro, halo and cyano and R" is alkylene of from 1 to about 50 carbon atoms, with (2) a dialkyl hydrocarbylphosphonate of the formula wherein R has from 1 to about 200 carbon atoms and is selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl and R is alkyl of from 1 to about 10 carbon atoms.

2. The composition of claim 1 wherein said copolymer is present in an amount of from about 0.005 to about 15% by weight of said oil.

3. The composition of claim 1 wherein said copolymer is prepared in the presence of an alkali metal.

4. The composition of claim 3 wherein said alkali metal is sodium.

5. The composition of claim 1 wherein said oil is a synthetic ester lubricating oil.

6. The composition of claim 5 wherein said ester is a pentaerythritol ester.

7. The composition of claim 6 wherein said pentaerythritol ester is prepared using a monocarboxylic acid having from 1 to about 20 carbon atoms.

8. The composition of claim 7 wherein the said acid is a mixture of acids containing from 5 to 9 carbon atoms.

9. The composition of claim 1 wherein the said arylimino dialkonal is 2,2-arylimino diethanol and the said dialkyl hydrocarbylphosphonate is dimethyl octadecylphosphonate.

References Cited UNITED STATES PATENTS 2,674,616 4/1954 Morris 252--32.5 X 2,683,691 7/1954 Thorpe et a1 252-325 X 3,542,679 11/1970 Cyba 252-325 X PATRICK P. GARVIN, Primary Examiner W. H. CANNON, Assistant Examiner US. Cl. X.R. 

